1. Field of the Invention
The invention relates generally to tuners and more specifically to a highly integrated tuner that can be configured for multiple mode operation and that can be highly integrated.
2. Background of the Invention
A key component in any television or set top box is the tuner. The tuner is the component that allows the television or set top box to tune into, or select, different channels. More generally, a tuner is a key component in any type of receiver that is configured to receive multiple channels. Thus, the tuner is configured to tune in the desired channel, while blocking or filtering signals on unwanted channels. The tuner is often also configured to filter received signals and block, or attenuate unwanted noise, or interference signals.
Clearly, the performance of the tuner will effect the overall performance of the television, or set top box. For example, if the tuner does not do a good job of blocking, or attenuating unwanted signals, or signals on unwanted channels, then the television, or set top box will not have “good reception.” Good reception is a clear product differentiator, especially with the advent of high definition television, which has raised the stakes, and profile with regard to reception quality for video consumer electronics. The tuner is often also one of the most expensive components in a television or set top box. Accordingly, tuner design is often driven by the need to improve performance, while reducing the cost. Reduced cost is often tied to reduced size, and increased component integration.
Much has been done in the area of tuner integration and increased performance; however, conventional tuners still suffer performance and integration limitations that effect the size, cost, and capability of conventional tuners, and therefore the products they ultimately go into.
FIG. 1 is a diagram illustrating a conventional receiver 100. It will be understood that a conventional receiver can comprise additional components beyond those illustrated. Such components are well known, however, and not relevant to the following descriptions and are therefore omitted for the sake of brevity. Receiver 100 can, for example, be included in a cable or terrestrial television or set top box. A receiver 100 is often interfaced directly with an antenna or cable input from which a multi-channel signal is received.
Conventional receivers can be configured to operate in accordance with one of the various digital and analog standards for both cable and terrestrial applications. The applicable standard defines the overall bandwidth of the system, and the channel scheme. In other words, each system is allocated a certain bandwidth. That bandwidth is then divided into a certain number of channels. Each channel is then defined by channel bandwidth and by a carrier frequency, or plurality of carrier frequencies.
For example, in the standard broadcast terrestrial system channels 2-13 are in the VHF band that extends from 54 MHz to 216 MHz and channels 14-83 reside in the UHF band that extends from 410 MHz to 890 MHz. The UHF band and VHF band are in the Radio Frequency (RF) portion of the frequency spectrum. Each channel in the standard broadcast terrestrial system has a 6 MHz bandwidth, i.e., the VHF and UHF bands are divided into a plurality of 6 MHz channels. Each channel is then associated with three carriers: one for video data, one for color data, and one for audio data. The video carrier is located at 1.25 MHz above the lower band edge, the color carrier is located 3.58 MHz above the video carrier, and the audio carrier is located 4.5 MHz above the video carrier.
A conventional receiver, such as receiver 100, often comprises several components including a front end tuner 102, a processor 104, as well as several other components including, for example, external filters 114 and 120. Tuner 102 typically comprises three stages: an RF stage 122, and Intermediate Frequency (IF) stage 124, and a low IF stage 126. RF stage 122 is configured to receive RF signals, e.g., in the VHF and UHF bands, and convert the RF signals to an IF signal for further processing. Many conventional tuners, such as tuner 102, are configured to actually up-convert the RF signal to a higher IF in order to reduce the amount of filtering needed at the input to tuner 102. IF section 124 can then be configured to convert the IF signal down to a lower IF signal for further processing by processor 104. Processor 104 can, for example, be configured to demodulate the low IF signal in order to recover the actual data, e.g., the video, color, and audio data. In other implementations, the demodulator can be separate from processor 104.
In RF section 122, the received signal is first filtered using a band pass filter 106, which is configured to filter out, or attenuate unwanted signals outside a desired bandwidth, or range of channels. The filtered signal is then often passed to a Low Noise Amplifier (LNA) 108. LNA 108 aids in the reception of very low power signals by amplifying the low power signal while adding very little noise itself to the amplified signals. The amplified signal is then typically amplified again by an Automatic Gain Control (AGC) amplifier 110. The gain of AGC 110 can, for example, be controlled by processor 104. The signal is then converted to an IF signal by mixer 112. Mixer 112 is configured to combine the received RF signal with a Local Oscillator (LO) signal in a manner design to produce the desired IF signal. The LO signal is tuned to the proper frequency based on the desired channel.
The IF signal is then filtered by filter 114 in IF section 124. Filter 114 is typically a Surface Acoustic Wave (SAW) filter. While SAW filters provide many advantages, their size and construction often prevent integration with other components, e.g., in tuner 102. The filtered signal is then mixed to a lower IF by mixer 118, which combines the IF signal with an IF LO signal. The IF LO signal is tuned to the proper frequency based on the desired channel.
The low IF signal is then filtered by filter 120 to remove unwanted image signals in low IF section 126 and ultimately passed to processor 104. Again, filter 120 is often an external SAW filter. The signal is then amplified by AGC 116.
As mentioned, conventional tuners, such as tuner 102, suffer several limitations. For example, conventional tuners often have an external SAW filter in the IF section, or low IF section that is application and standard specific. In other words, the bandwidth of, e.g., filter 120 is defined based on the standard that tuner 100 is configured to implement. For example, in the U.S. the TV and digital cable channels are 6 MHz apart so the appropriate SAW filter would be a 6 MHz filter. In the Europe, the TV and digital cable channels are 8 MHz apart so that the appropriate SAW filter is 8 MHz. As a result, a tuner that is designed to work in the U.S., with a 6 MHz SAW filter, will not work as a tuner designed to work in Europe and vise versa. As a result, tuner manufacturers have to build different TV tuners depending on the end market and cannot build a single off the shelf tuner for use anywhere in the world.
Additionally, in conventional tuners, the RF and IF AGCs, e.g., AGCs 110 and 112 respectively, are used to adjust the power level of the low IF signal to a fixed value, regardless of the power level for the signal at the input to the tuner. Conventional tuners use what is called a take over point algorithm to adjust the RF AGC and IF AGC of the tuner over the dynamic range of corresponding standard. Although this technique is simple to implement, it lacks flexibility and can often result in less than optimum performance under various and different RF environments, especially in terrestrial applications.
For example, the take over point technique assumes a fixed and predefined RF condition for the tuner and then optimizes the RF and IF AGC settings for this assumed condition. Often, the assumed condition is a worse case condition in order to ensure that the receiver will work under such a worse case condition. If the tuner experiences a different RF condition, however, then the assumed conditions will obviously be incorrect. This can actually have an adverse effect on performance, since the AGC settings will not be optimized for the actual conditions. In the case where the assumed condition for the AGCs take over point is a worse case condition, the tuner will actually be experiencing better conditions most of the time. As a result, a conventional tuner's performance will not be optimized under most conditions, making it high likely that the Signal-to-Noise Ratio (SNR) at the output of the tuner is not what the tuner could deliver if the take over point could have been adjusted for the actual conditions. The inability to adjust the take-over-point in conventional tuners can have a particularly adverse effect in terrestrial applications where the RF environment varies from location to location and time to time.